Fun with Algebraic Effects – From Toy Examples to Hardcaml Simulations

A Jane Street engineer just swapped a hardware-simulation helper from the old “monads” style to shiny new “algebraic effects,” a feature in OCaml 5. Translation: fewer hoops to jump through, more readable code, and a claim that the new way is simply more elegant. There’s even a rename underway—Oxcaml_effect is becoming Handled_effect—and yes, the peanut gallery noticed. The post argues that what monads do, effects can do more cleanly, especially for simulations that need to pause and resume.

Cue the comments. The thread split into three moods: the “finally, less boilerplate!” crowd; the “don’t toss monads, they’re battle-tested” skeptics; and the pragmatic middle who say “use what fits.” One reader dropped a serious homework link to a book chapter on effects vs monads and name-dropped a model-checking tool for extra cred, turning the discussion from hype to homework. Meanwhile, the meme machine fired up: folks joking that effects are “monads without the ceremony,” others teasing that renaming libraries is the real hard problem. Underneath the jokes, the core fight is about clarity vs control—do you want code that reads like normal flow, or code that makes every step explicit? Either way, OCaml’s new trick just stole the spotlight, and the devs brought receipts with Handled_effect and links to deep dives like this book.